In “The Demographic Transition Theory of War,” Deborah Jordan Brooks, Stephen Brooks, Brian Greenhill, and Mark Haas set out to show that the likelihood of experiencing the onset of interstate conflict shifts dramatically downward as states pass through a demographic transition. Demonstrating this trend statistically is no easy task. Interstate conflicts are rare events, which typically involve a confusing multi-state mix of actors. Yet, Brooks and her colleagues, who make some innovative methodological choices, succeed in convincingly demonstrating that this expected downward trend can be observed in at least four standard demographic measures—median age, the youth-bulge ratio, total fertility rate, and life expectancy at birth. Perhaps most interesting, for their set of interstate conflict data (1960 to 2001) the authors find that the peak probability of onset for interstate conflict is not at the earliest extremes of these variables.

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